The invention relates to a method of manufacturing a frame-mounted membrane and to membrane pumps and membrane valves utilizing membranes manufactured in this manner.
A method of making a thin membrane is known from German Patent DE 39 20 788 C1 and also from a publication "Mikromembranen fer beruhrungslose Messungen mit Ultra-schall" (Micromembranes for Contact-free Measurements with Ultrasound) by W. K. Schomburg, M. Walter, R. Kohler, and V. Liebig, VDI--Berichte No. 939 (1992), pages 543-548. The publication describes the manufacture of honeycomb-like micromembranes of titanium which have a thickness of 3 .mu.m and lateral dimension of about 80 .mu.m and which are freely mounted on a frame. Those micromembranes had a resonance frequency of 3 Mhz. The resonance frequency is dependent, among other factors, on the temperature, the membrane tension and the differential pressure on the membrane, so that these parameters can be determined with such a membrane. The frame-mounted micromembranes are manufactured in the following manner:
On a silicon wafer which serves as a substrate, a membrane layer is so deposited that it can be easily separated therefrom. For this purpose, an about 100 nm thin separation layer of carbon is first applied to the silicon wafer, wherein an edge section of the silicon wafer of about 3 mm is left uncoated. Then a 3 .mu.m thick layer of titanium is deposited thereon by magnetron spattering which attaches to the silicon wafer only at the uncoated edges. On this membrane layer, a relatively thick honey-comb nickel structure of at least 10 .mu.m in thickness is formed by the known process of x-ray depth lithography with subsequent galvanic forming. Around the nickel structure, a solid raised frame is bonded to the membrane layer and the membrane layer is removed from the silicon wafer along the edges. Then there is no firm connection left between the membrane layer and the silicon wafer so that the silicon wafer can be removed from the membrane layer in a special device by subjecting it to a slight bending. In this manner, a frame-mounted membrane is obtained, which is divided by the nickel structure into micromembranes.
With the known method, membranes with uniform properties are obtained. The lateral deflection of the membranes is determined, among others, by the membrane dimensions, the membrane thickness, the inner mechanical tension and the modulus of elasticity of the membrane. For certain applications such as the manufacture of micromembrane pumps or micromembrane valves, frame-mounted membranes with locally different properties are more advantageous. It may, for example, be advantageous for a micromembrane pump if the membrane is more resilient in the area of the pump chamber than in the area of the supply lines and the valves. Furthermore, a particular material property such as electric conductivity may be important for the manufacturing process of a membrane pump, whereas in the areas of the valves or the pump membrane, other properties such as resiliency are most important and that all these properties cannot be optimized for a particular location.
It is, therefore, the principal object of the present application to provide a method of manufacturing a frame-mounted membrane which can have different physical properties at predetermined locations.